Hydrography and Bathymetry Sounding Methods
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1
Measurement of the depth of the bed below the water surface at a particular point
Sounding
2
Depiction of the topography (depth) of the seafloor
Bathymetry
3
The shape of the bottom of a water body
Bed profile
4
Sounding methods that touch the bed, such as rods and lead lines
Direct methods
5
Sounding methods that use acoustic techniques with transducers
Indirect methods
6
Graduated pole that gives depth directly from the reading at the water surface
Sounding rod
7
Part fitted at the bottom of a sounding rod to keep it vertical
Arrow or lead shoe
8
Sounding rod graduations are numbered from this end
Bottom upward
9
Rope with a plummet at its end used to measure depth
Lead line
10
The most primitive tool in depth measurement
Lead line
11
Person who manually casts the lead line
Leadsman
12
Materials used to mark lead line graduations
Cloth or leather tags
13
Weight at the end of a lead line, usually made of lead
Plummet
14
Effect of current that makes a lead line reading greater than the true depth
Drag
15
Improved version of the lead line with a barrel, flexible wire and winding handle
Sounding machine
16
Maximum depth for which a sounding machine is useful
30 meters
17
Device in sonar that converts electric energy into high-frequency sound
Transducer
18
Sound Navigation and Ranging
SONAR
19
The most common equipment used in indirect depth determination
Echosounder
20
Echosounder unit that emits underwater supersonic pulses
Transmitter
21
Echosounder unit actuated by echoes reflected from the bed
Receiver
22
Echosounder that measures the time between emitted sound and returning echo from a small area under the boat
Single Beam Echosounder (SBES)
23
Another name for the single beam echosounder
Fathometer
24
The sonar pulse emitted from the transducer
Ping
25
Filling a small area beneath the boat with sound
Ensonifying
26
Small area beneath the boat ensonified by an SBES
Footprint
27
Echosounder with a wide angular lateral aperture transducer
Multi-beam Echosounder (MBES)
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Echosounder that maps a contiguous strip perpendicular to the vessel’s path
Multi-beam Echosounder (MBES)
29
Echosounder that uses a sweep system, designed for canals, rivers and shallow water
Multichannel Echosounder (MCES)
30
Width of the seafloor strip covered by MBES or MCES
Swath width
31
Which echosounder is designed for canals and rivers?
- Multichannel Echosounder (MCES)
- Single Beam Echosounder (SBES)
- Multi-beam Echosounder (MBES)
- Sounding machine
32
Formula for depth from velocity of sound and time interval
$h=\frac{vt}{2}$
33
Symbol for velocity of sound in the echosounder formula
v
34
Symbol for the time between transmission and reception of the signal
t
35
Inclined distance measured by an echosounder before correction
$h'=\frac{vt}{2}$
36
Formula for actual depth when the transmitter and receiver are separated by d
$h=\sqrt{(h')^2-(d/2)^2}$
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Symbol for the distance between the transmitter and receiver
d
38
Type of area where the separation correction is significant
Shallow areas
39
Type of area where the separation correction is negligible
Areas of great depth
40
Height or depth of a point above or below any datum
Reduced level (R.L.)
41
Instrument used to determine the water surface level at the time of sounding
Tide gauge
42
Datum commonly adopted as the chart or fixed datum in navigation
Mean Lower Low Water (MLLW)
43
Symbol for the measured sounding in the datum figure
ac
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Symbol for the gauge reading in the datum figure
D
45
Symbol for the reduced sounding in the datum figure
h
46
Formula for reduced sounding
$h=ac-D$
47
Measured sounding minus gauge reading
Reduced sounding
48
Time interval at which the recorder takes gauge readings
Every 5 minutes
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Gauge reading at MLLW minus gauge reading at the time of sounding
Gauge reading correction
50
Sign of the correction when the assumed datum gauge reading is greater than the actual reading
Positive
51
Sign of the correction when the assumed datum gauge reading is less than the actual reading
Negative
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Meaning of a negative corrected sounding
Point is above the datum
53
Reduced sounding when measured sounding is 12 m and gauge reading is 4 m
8 m
54
Gauge reading correction when MLLW reading is 3 m and sounding-time reading is 4 m
-1.00 m
55
Conventional method using a horizontal wire towed between two ships and supported by buoys
Wire drag
56
Shape the wire forms when it hits an obstruction in wire drag
V shape
57
Approximate interval of wooden floats on a wire drag
30 m
58
Modification of wire drag with non-adjustable cables and no intermediate floats
Wire sweep
59
Conventional method used where few obstructions are expected and water is deeper than needed for navigation
Wire sweep
60
Rail, beam or steel pipe suspended by two vertical cables to find minimum clear depths
Sweep bar
61
Conventional method suited for river channels and constricted areas
Sweep bar
62
Equipment that detects seafloor objects but cannot determine depth
Side-scan Sonar (SSS)
63
Apparatus towed behind the boat that sends the side-scan transmission signal
Towfish
64
Three components of side-scan sonar
Processing unit, towfish and transmission cable
65
Ranges shown in the side-scan sonar figure
Slant range and ground range
66
Sonar with a bow-mounted transducer for navigation and obstacle avoidance
Forward-Looking Sonar (FLS)
67
Sonar whose data are displayed in 3D on a graphical user interface
Forward-Looking Sonar (FLS)
68
Components of forward-looking sonar
Transducer, power module and graphical user interface
69
Satellite method that analyzes spectral changes from sunlight reflectance
Optical remote sensing
70
Remote sensing that cannot penetrate clouds
Optical remote sensing
71
Satellite sensor that uses centimeter to meter wavelengths and penetrates clouds
Synthetic Aperture Radar (SAR)
72
Data still required for satellite seafloor classification
Ground truth data
73
Laser-based sensor that uses green and red or infrared lasers
Light Detection and Ranging (LiDAR)
74
Laser color used for bathymetric data in LiDAR
Green
75
Typical wavelength of the green LiDAR laser
532 nm
76
Maximum water depth penetrated by green LiDAR light
About 70 meters
77
Near-IR wavelength shown in the LiDAR figure
1064 nm
78
LiDAR laser that reflects off the water surface to map the adjacent shore
Red or infrared laser
79
Water condition in which LiDAR does not apply
Chronic moderate to high turbidity
80
Tide period favorable for scheduling LiDAR operations
Neap tide
81
Typical LiDAR sounding rate
900 Hz (3.24 million soundings per hour)
82
Typical LiDAR area coverage
20 km² per hour
83
Typical LiDAR swath width at 400 m flight altitude
240 m
84
Typical LiDAR bathymetric depth range
-70 m to -0.5 m
85
Maximum topographic height of bathymetric LiDAR
+50 m
86
IHO standard followed by LiDAR depth accuracy
S-44, 4th Edition 1998, Order 1
87
LiDAR position accuracy
5 m CEP at 95%
88
Probability that the true horizontal position lies inside a circle of radius 5 m
Circular Error Probable (CEP)
89
Which sensor detects objects but cannot give depth?
- Side-scan Sonar (SSS)
- Multi-beam Echosounder (MBES)
- Bathymetric LiDAR
- Single Beam Echosounder (SBES)
90
Which sensor has a bow-mounted transducer for obstacle avoidance?
- Forward-Looking Sonar (FLS)
- Side-scan Sonar (SSS)
- Sweep bar
- Synthetic Aperture Radar (SAR)
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